Safety switching system for clamping devices for pipes

ABSTRACT

The invention relates to a safety switching system for a clamping device, provided with clamping wedges and operable by a flowing medium for holding and/or lowering or raising a pipe string, with which a borehole is lined in order to support the rock and create a transport line, characterized in that there is attached to a clamping wedge holder of the clamping device a trip cam for a safety switching valve which is mounted at the basic body of the clamping device and is actively connected to the trip cam when the clamping wedges assume their prescribed clamping position on the pipe string. In another aspect, a safety switching system for use with a string of tubulars may include a clamping device having one or more movable wedges for clamping the tubular; a cam member attached to one of the one or more movable wedges, the cam member movable therewith and includes a switching surface and one or more ramp surfaces, and a safety switch disposed on an adjacent surface, the safety switch constructed and arranged to become actuated by the cam member when the string of tubulars is in a predetermined position within the clamping device.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO A MICROFICHE APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

Field of the Invention

Description of the Related Art including information disclosed under 37CFR 1.97 and 1.98

The invention relates to a safety switching system for a clampingdevice, provided with clamping wedges and operable by a flowing mediumfor holding and/or lowering or raising a pipe string with which aborehole is lined in order to support the rock and create a transportline.

When creating a pipe string and lowering it into a borehole, clampingdevices absorbing the considerable inertia forces of the pipe string arealternately used. One of the devices is a holding apparatus (spider),with which a pipe string is held with the help of clamping wedges forscrewing to another pipe. For such a holding apparatus, according toU.S. Pat. No. 2,545,177, an apparatus for automatic control of theplacing of the clamping wedges is used when the desired position of thepipe string has been reached.

The fitting of an individual pipe onto a pipe string takes place firstlywith an auxiliary elevator, which transfers the pipe from a pipe store,places it onto the pipe string and holds it there during the screwingprocess. After the end of the screwing to the pipe string positionedunder the fitted-on pipe, the auxiliary elevator is removed and replacedby the second clamping device, an elevator. This is essentiallyconstructed identically to the holding apparatus and is pushed fromabove over the initially exposed pipe which is already screwed to thepipe string, until its clamping wedges reach the prescribed position onthe pipe. Its clamping wedges are then put in place.

In practice, reaching the correct position on the pipe is difficult. Theelevator does not allow a precise observation for determining thecorrect position of its clamping wedges. For example, gripping part of apipe sleeve can lead to a slip during the assumption of the very highinertia forces and to considerable damage to the pipe sleeve, as it isto be taken into account that the elevator must hold the entire pipestring at the top end of a screwed-on pipe and lower it as soon as theholding apparatus (spider) is released from the pipe string. This isachieved by the elevator firstly raising the entire pipe stringsomewhat, to relieve the holding apparatus. Only then can its clampingwedges be released, for example with the help of compressed air.Furthermore, a misunderstanding is to be prevented which causes theholding apparatus (spider) to be opened, although the elevator is notyet closed, and a pipe held by the spider or even a longer pipe stringto thereby be lost.

The loss of a pipe string through incorrect use of the elevator or amis-opening of the spider entails high costs and must therefore beavoided. Therefore, with a safety apparatus according to DE 42 27 645C2, a possibility was created of placing the clamping wedges of anelevator on the pipe as soon as a pipe sleeve enters the range of acontact switch. This switching device is mounted on the upper side ofthe elevator. Mechanical influences which can lead to a defect are notto be ruled out however and threaten the necessary high switchingsecurity.

BRIEF SUMMARY OF THE INVENTION

The object of the invention is to create a safety switching system ofthe sort mentioned at the beginning which is arranged protected inside aclamping device, is not subjected to outside mechanical influences andrules out faulty switching with certainty. The invention for achievingthis objective is distinguished by the fact that there is attached tothe clamping wedge holder of the clamping device a trip cam for a safetyswitching valve, which is arranged at the basic body of the clampingdevice and is operable by the trip cam which is moveable with theclamping wedge holder when the clamping wedges assume their prescribedclamping position on the pipe string.

Preferably, the trip cam has a run-on ramp, a run-off ramp and avertical switching surface located between these and can be traversed bya contact wheel of the switching valve.

The length of the switching surface is determined by the differences indiameter between the largest and the smallest of the pipes to be clampedas prescribed with the clamping device.

For use on an oil-rig using two alternately operable clamping devices(spider and elevator) it is proposed that the safety valve of one deviceis placed upstream of the control valve for the actuation of the workingcylinder for clamping wedges of the other device.

Additionally, a short-circuiting switch is provided for every clampingdevice to bypass the safety switch. This switch is actuated to be ableto introduce a clamping action at the first pipe of a pipe string to beformed.

The use of additional safety valves which reciprocally stop the controlcylinders for the opening and closing of the clamping devices becomingactive at the same time and accordingly prevent a simultaneous openingof both clamping devices, for example in the case of simultaneouslyfaulty switching, is of further considerable significance as regardssafety.

The individual components of the safety switching system are ofextraordinary simplicity, developed in a manner customary in the market,and housed in a clamping device so that mechanical defects cannot arisefrom outside influences. Faulty switchings are ruled out with a highdegree of certainty.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

In the drawing, an embodiment of the invention is schematicallyportrayed and further explained. These are shown in:

FIG. 1 a sketch illustrating the principle of the safety switch withtrip cam.

FIG. 2 a cross-section through a clamping device before the start of aclamping process.

FIG. 3 the clamping device according to FIG. 2 with wedges in place andan incorrect pipe position.

FIG. 4 the clamping device according to FIGS. 2 or 3 with clampingwedges in place after reaching the correct pipe position inside thedevice.

FIG. 5 the wiring diagram for a pneumatically-operated safety switchingsystem.

DETAILED DESCRIPTION OF THE INVENTION

The safety switch 1 with its housing 2 is firmly connected to a clampingdevice (not shown) and carries, at the front end of holding arm 3, acontact wheel 4 by which the surfaces 5, 6 and 7 of a trip cam 8 can betraversed.

The surfaces 5 and 7 are run-on surfaces for the contact wheel 4 andpass into the switching surface 6. A length “I” of the run-on surfaces5, 7 is calculated according to the differences in diameter between thelargest and the smallest of the pipes (not shown) which are to beclamped by the clamping device in the prescribed way. The cam 8 moves inthe direction of the double arrow 9 through its fixed connection toclamping wedges 12 a, 12 b of the clamping device and, when activelyconnected to the touching wheel 4, allows the latter to reach itsswitching position via the surfaces 5 and 6.

In the embodiment shown according to FIG. 1 the safety switch 1 is notportrayed in the contact position with the trip cam 8 for reasons ofbetter clarity.

Two clamping wedges 12 a and 12 b are arranged for example verticallypositionable inside a basic body 10 with wedge surfaces 11. Betweenthese wedges there is a section of a pipe string 13 which is to begripped and clamped by positioning the wedges 12 a, 12 b.

The clamping wedges 12 a, 12 b are fixed to wedge holders 14 a and 14 band linked to an annular holding member 17 via power-transmission barsand connectors 16 a and 16 b. The annular holding member 17 isvertically adjusted via positioning units consisting of workingcylinders and positioning pistons 18 a and 18 b. The positioning units18 a, 18 b can be both pneumatically and hydraulically actuated. A feedline for the medium is indicated for example by 19. The feed 19 iscontrolled via a working valve 20, whose actuation lever 21 ismechanically connected to a control cylinder 22. A protective cover 23on the base 10 very largely seals off the entire apparatus to theoutside.

FIG. 2 shows a part of the pipe string 13 with a pipe sleeve 24 insidethe still opened clamping wedges 12 a, 12 b. However, the greaterdiameter of the tube sleeve 24 prevents the positioning of the clampingwedges 12 a and 12 b in their prescribed position. The trip cam 8 willnot thus reach the contact wheel 4 of the safety switch 1. The sameeffect will come about with a clamping process with a pipe 13 which ispositioned in the prescribed way, but has too great a dimension.

Another incorrect position of the pipe string 13 inside a clampingdevice is shown in FIG. 3. The pipe string 13 to be clamped has notreached the clamping wedges 12 a and 12 b. Upon actuating of thepositioning units 18 a and 18 b, the clamping wedges 12 a, 12 b cantherefore be quickly lowered to the bottom end of the wedge surface 11.The trip cam 8 thereby runs quickly past the contact wheel 4, so thatthere is no effective switching process, to be triggered by the safetyswitch 1, which releases the positioning units of the second clampingdevice (not shown). The effect will be the same in a clamping processwith a pipe 13 which is correctly positioned but has too small adiameter.

FIG. 4 shows the pipe string 13 in the prescribed clamping positioninside the clamping device. The clamping wedges 12 a, 12 b grip the pipestring 13 underneath the connection sleeve 24. The clamping wedges 12 a,12 b can carry out the clamping process with the help of the positioningunits 18 a and 18 b and in doing so assume their prescribed positionwithin the clamping wedge surface 11. With the lowering of the clampingwedges 12 a and 12 b, the trip cam 8 fixed to the holding member 14 b ofthe clamping wedge 12 b enters the range of the contact wheel 4 andpresses it against the housing 2 of the safety switch 1. The contactwheel 4 is actively connected to the holding surface 6 of the trip cam8, this not being able to be moved further down so that the contactwheel 4 always lies against the holding surface 6 and raises the lockingdevice above the control cylinder of the second clamping device (notshown) so that this can release the pipe string 13.

The switching elements provided for the desired automatic running of theworking processes on an oil rig with a holding apparatus (spider) 31 anda lowering and a raising apparatus (elevator) 32 are contained within aswitch box 30 (FIG. 5). The corresponding connection lines lead from theswitch box 30 to the safety valves 1 and 101 on the holding device 31and on the lowering and raising apparatus (elevator) 32 as well as tothe corresponding control cylinders 22 and 122, which are each locatedon the devices. The components of the entire safety system will beexplained in the following by reference to the individual process stepswith the beginning of a screwing process. For the sake of simplicity,the lowering and the raising device 32 is given the customary name“elevator” and the holding device 31 the name “spider” as is customaryin the industry.

The entire apparatus is supplied with compressed air via the pressuresource 40. Firstly, the spider 31 and the elevator 32 are closed. Thesafety bypass valve 41 for the spider 31, which is closeable by hand, isopened. The identical safety bypass valve 141 for the elevator 32 canremain closed. Thereupon the actuation valve 42 for the spider 31 trips.This opens the spider 31. With an auxiliary elevator (not shown), a pipe(not shown) can be threaded into the spider 31. The spider 31 is thenclosed via the actuation valve 42, assuming the trip cam (not shown)reaches and maintains its switching position. The safety bypass valve 41is then switched off and secured, whereby the safety system is switchedon via the safety switch 1.

A further pipe (not shown) is fitted onto the pipe held in the spider 31with the auxiliary elevator and screwed on. The opened elevator 32 canthen be pushed over the screwed-on pipe. By pressing the actuationswitch 142, the elevator 32 closes over the control cylinder 122 andclamps the screwed-on pipe. The safety switch 101 on the elevator 32 isactivated via the trip cam. Thereby, the mediums' path to the actuationvalve 42 is freed.

The spider 31 can then be opened by pressing the actuation valve 42. Theassociated trip cam 8 leaves the switching position on the safety valve1. The medium to the actuation valve 142 is blocked off and emptied. Theelevator 32 can now lower the pipe string formed by the first twoscrewed pipes into the desired position. The switch 42 is then actuatedagain, whereby the control cylinder 22 is activated and the spider 31closes. After the trip cam has reached its prescribed position, thesafety switch 1 clamps again, so that the elevator 32 is freed foropening again.

The valves 43 and 143 are safety valves which reciprocally prevent thecontrol cylinders 22 and 122 from being able to be actuatedsimultaneously and the clamping wedges 12 a, 12 b thereby released fromthe spider 31 and elevator 32 simultaneously.

The two valves 43, 143 can be blocked by shut-off valves 44 and 144 onorder to be able to introduce a working procedure with the housing ofthe first pipes in the spider 31 and elevator 32.

What is claimed is:
 1. A safety switching system for a clamping device,provided with clamping wedges and operable by a flowing medium forholding and/or lowering or raising of a pipe string, with which aborehole is lined in order to support rock and create a transport line,characterized in that there is attached to a clamping wedge holder (14a, 14 b) of the clamping device a trip cam (8) for a safety switchingvalve (1) which is mounted at the basic body (10) of the clamping deviceand is actively connected to the trip cam when the clamping wedgesassume their prescribed clamping position on the pipe string, therebymaintaining the clamping wedges in their prescribed clamping position.2. The safety switching system according to claim 1 for use on an oilrig using two alternately actuatable clamping devices, characterized inthat the safety switching valve of a lowering and a raising device isplaced upstream of the control valve for the actuating of the workingcylinder for clamping the wedges of a holding device.
 3. The safetyswitching system according to claim 1, wherein the trip cam (8) includesa run-on ramp, a run-off ramp and a vertical switching surface (6)situated between them and can be traversed by a contact wheel (4) of thesafety switching valve.
 4. The safety switching system according toclaim 3, wherein the length (1) of the run-on (5) and run-off ramp (7)is determined by the difference in diameter between the largest and thesmallest of the pipes which can be clamped by the clamping device. 5.The safety switching system according to claim 2, characterized in thata bypass switching valve (41, 141) is provided for every clamping deviceto bypass the safety switch.
 6. The safety switching system according toclaim 2, characterized in that safety valves (43, 143) are placedupstream of the control cylinders (22, 122) for positioning the clampingwedges of the two clamping devices, in such a way that, upon actuationof the control cylinder of one clamping device, the control cylinder ofother device is blocked.
 7. The safety switching system according toclaim 6, characterized in that shut-off valves (44, 144) are placedupstream of the safety valves (43, 143) for the switching off of thesafety valves and the shut-off valves can be operated by the actuationof the bypass valves (41, 141) for the bypassing of the safety switches.8. The safety switching system according to claim 6, characterized inthat the safety valves (43, 143) and shut-off valves (44, 144) areprovided with return springs for automatic repositioning after arelieving of pressure.
 9. The safety switching system according to claim1 for use on an oil rig using two alternately actuatable clampingdevices, characterized in that the safety switching valve of a holdingdevice is placed downstream of the control valve for the actuating ofthe working cylinder of a lowering and raising device.
 10. A safetyswitching system for use with a string of tubulars, the systemcomprising: a clamping device having one or more movable wedges disposedtherein for clamping the tubular string; a cam member attached to one ofthe one or more movable wedges, the cam member movable therewith andincluding a switching surface and one or more ramp surfaces; and asafety switch disposed on an adjacent surface, the safety switchconstructed and arranged to become actuated by the cam member when apredetermined diameter of the string of tubulars is within the clampingdevice.
 11. The safety switching system of claim 10, wherein a length ofthe one or more ramp surfaces is determined by a difference between afirst diameter and a second diameter of the string of tubulars.
 12. Thesafety switching system of claim 10, wherein actuating the safetyswitching system comprises moving the cam to a position whereby the camis in contact with the switching surface.